Erythropoietin (hereinafter referred to as EPO) is an acidic glycoprotein hormone which promotes the differentiation and proliferation of erythroid progenitor cells. This hormone is secreted chiefly by the kidney. Erythrocytes are present abundantly in the blood for certain periods, and are then destroyed by the spleen, etc. (their mean life in humans is about 120 days). However, red blood cells are constantly supplied from the bone marrow, so that the peripheral total erythrocyte count is kept constant in a normal state. EPO plays a central role in maintaining such homeostasis of erythrocytes in the living organism.
High purity human urinary EPO was obtained by purification from a large volume of urine from patients with a plastic anemia. This enabled cloning of human EPO gene. Nowadays, it has become possible to produce a large amount of recombinant human EPO in animal cells by genetic engineering technology. The applicant of this invention has succeeded in producing a preparation (lyophilized preparation) of the purified EPO, and supplies it to the market in the form of renal anemia alleviating agents and so on.
Drug design for supplying the market with stable EPO preparations requires that chemical changes (hydrolysis, disulfide exchange reaction, etc.) or physical changes (denaturation, agglutination, adsorption, etc.) observed with EPO be suppressed. Products now on the market contain human serum albumin or purified gelatin which is generally used as a stabilizer. These substances have been added in these products to suppress chemical or physical changes. Since human serum albumin is a blood product relying on donated blood for its supply, the necessity for its addition has been questioned. Regarding the addition of a protein other than the albumin or gelatin as a stabilizer, it is difficult to avoid the risk of viral contamination completely.
Peptide drugs are often lyophilized for stabilization. However, lyophilization increases manufacturing costs, and involves an increased risk due to mechanical troubles.
For the foregoing reasons, demand is growing for an EPO preparation as an alternative to a lyophilized preparation, the EPO preparation being free from inclusion of a protein as a stabilizer, and stable during long-term storage.